TEDD

TEDD is an acronym for Thermal Equalization and Distribution Device. It is designed to reduce the wide temperature variation across the diameter of the melt stream as it exits the extruder. The temperature can have a variety of profiles depending on machine speed and screw design.

Peak to peak variations as much as 30o F are common and this translates into large viscosity variations. Cut and try modifications must be made to the die to produce the product profile required. This means the die will produce the right profile over a rather limited production rate range.

The TEDDÒ takes advantage of the fact that the temperature profile exiting the die is symmetrical about the axis of the machine. It turns the melt flow inside out several times just before the melt arrives at the die. This periodically moves hot material to a relatively cold zone and vice versa. Temperature variations are substantially reduced, melt viscosity is now constant, and the die will perform consistently over a wide production rate range.

VISCOSITY AND PRESSURE DROP CONSIDERATIONS

Most polymeric materials are shear sensitive. That is to say, their viscosity is dependent on the shear rate to which they are exposed. Usually an increased shear rate produces a lowering of viscosity and is referred to as shear thinning. Viscosity versus shear rate data is usually provided by the polymer manufacturer in the form of a graph on log/log paper. We list below the shear rate and pressure drop formula for each of the devices we have described and others together with the units involved.

Main pipe inside diameter = D inches
Main product flow rate = Q gpm
Shear rate = g sec-1
Viscosity = m cP
Pressure drop = dP psi
Axial length = L inches
Additive fraction = F
Number of mixing elements = n

Device A/t Value Shear rate Pressure drop Comments
Open pipe ---------- 39.2Q/D3 22.73x10-6Qm L/D4 Hagen-Poiseuille Equation
Helix np 96.0Q/D3 205x10-6Qm n/D3 Helix L/D ratio = 1.5:1
L/H unit 8/p2 F 215Q/D3 5.9x10-4Qm /D3 Each hole dia. = 0.45D
H/L unit 3.6/F 81.7Q/Dt2 22.1Qm L/Dt3 Where annulus dia.= 2D/3

KOMAX SYSTEMS, INC. INTRODUCES
A NEW STATIC MIXER SYSTEM

FOR HIGH VISCOSITY PRODUCTS

(U.S. Patent 5,484,203)
  • A Single Injection Point allows pressurized clearing action from the additive pump if needed. The built in check valve prevents back flow of polymer into the additive supply.
  • The TADD Injector distributes additive across the inlet of the ULTRA mixer. It is less than one pipe diameter in length and has a low pressure drop.
  • The ULTRA Mixer generates multiple interstices with a uniform spatial distribution to give 100% utilization of the mixer volume and superior additive dispersion with low pressure drop

Device A/t Value Shear rate Pressure drop Comments
SIDD 288/p2 F 593Q/D3 12.6x10-4 Qm /D3 Each hole dia. = 0.3D
PARAFLO 8pN/F Contact factory for shear rate and pressure drop calculations.

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